1. Field of the Invention
The present invention generally relates to an antenna.
2. Description of Related Art
In recent years, as continuous demand for wireless devices for mobile communication remains, various communication systems have been developed, and high performance, small, light-weight wireless devices that comply to a plurality of communication systems using a single integrated unit are in demand as well. Accordingly, there is an inevitable demand for development of antennas equipped in these wireless devices.
As a result, Planar Inverted-F Antennas (PIFAs) and Reverse-Fed Planar Inverted-F Antennas (RFPIFAs) have been designed. Referring to FIG. 10, a PIFA antenna 10 includes a ground plane 11, a match portion 13, a radiation portion 15, a feeder line 17, and a stub 19. The ground plane 11 defines a feed hole 111 therein. The match portion 13 and the radiation portion 15 are parallel to the ground plane 11. One end of the feeder line 17 is connected to a feed point 131 between the match portion 13 and the radiation portion 15, while another end of the feeder line 17 passes through the feed hole 111. One end of the stub 19 is connected to a shorted end 133 of the match portion 13, while another end of the stub 19 is connected to the ground plane 11.
The radiation portion 15, the feeder line 17, the feed point 131, and the ground plane 111 form a capacitor area of the PIFA antenna 10. The match portion 13, the feeder line 17, the feed point 131 and the stub 19 form an inductor area of the PIFA antenna 10. Also referring to FIG. 11, an equivalent circuit of the PIFA antenna 10 is shown. A first terminal 180 is equivalent to the feed point 131, while a second terminal 190 is equivalent to the ground plane 11 A capacitor C is equivalent to the capacitor area of the PIFA antenna 10, while an inductor L is equivalent to the inductor area of the PIFA antenna 10. Therefore, the antenna 10 is equivalent to an LC circuit. Furthermore, referring to FIG. 12, an RFPIFA antenna 10′ is also illustrated. In comparison with the PIFA antenna 10, a shorted end 133′ is connected between the match portion 15′ and one end of a match portion 13′, while a feed point 131′ is connected to another end of the match portion 13′.
However, the ground planes used in the PIFA antenna 10 and the RFPIFA antenna 10′ determine main sizes of the antennas, and it is necessary to minimize the ground planes.
Therefore, improvements for an antenna are needed in the industry to address the aforementioned deficiency.